1. Field of the Invention
The present invention relates to a scheme for information delivery to mobile computers which enables mobile computers to acquire WWW (World Wide Web) information from WWW information servers through wireless accesses.
2. Description of the Background Art
In conjunction with the development of smaller and cheaper computer systems and improved network environment, the use of computer systems has rapidly spread to various fields, and in particular the use of the world's largest computer network called the Internet has spread in recent years such that many people are now accessing the Internet to utilize information or services available on the Internet.
On the other hand, in conjunction with the spread of such networks, the technique of the mobile computing has been developing actively. In the mobile computing, a user who carries a portable terminal or computer carries out communications while moving over networks. There are cases where a user's location on networks changes while communications are carried out, and for the communication access from a visited site, not only the conventionally used wired networks but also wireless networks such as those of the cellular telephone and the PHS (Personal Handy phone System) can be utilized.
On the Internet, the information delivery scheme in the hypertext format called WWW is mainly utilized. This is a scheme which uses the language called HTML (HyperText Markup Language) by which links can be set up between mutually related information such that one can jump from one information (Web page) to another easily. Also, by using this WWW, it is possible to realize information exchanges in diverse forms such that, besides a simple information providing from a WWW server, it is possible for a WWW server to receive inputs (such as answers to questionnaire, ticket reservations, orders for commercial goods) from users on client devices (terminals or computers), and it is also possible to send information using image data and speech data. Consequently, it is possible to construct a framework for the electronic commerce, for example.
Accesses to the WWW are basically realized by communications between a client device and a WWW server using the TCP/HTTP protocol. However, in general, if accesses to all relevant WWW servers are made in response to access requests with respect to various WWW pages issued from various client devices, the amount of traffics on the networks would become enormous and the network bandwidth would be wasted, so that a longer access response time would be required. Also, when many accesses are concentrated on a specific WWW server, the performance of that WWW server can be degraded.
In order to avoid these problems, there is a provision to provide cache servers (also called proxy servers) for caching (temporarily storing) necessary WWW page contents nearby client devices. In this provision, it becomes unnecessary to carry out communications with WWW servers for every access, by constantly maintaining popular, high hit rate (frequently accessed) pages in the cache servers, so that the traffics can be reduced and the response time can be shortened. This cache scheme is particularly effective when the network bandwidth on the terminal side is limited as in the case of using a portable terminal via wireless accesses.
As described above, in the case of the mobile access to the Web via the Internet using a wireless portable terminal, if accesses to the WWW servers are made every time, the response time would become long so that it cannot be expected to utilize information services comfortably because the wireless network bandwidth on the terminal device side is limited.
In order to avoid this problem, there is a need to cache Web pages in cache servers provided on an access route so as to shorten the response time and reduce the amount of traffics on the network.
In such an information delivery system, one or a plurality of cache server devices are provided on appropriate locations on the network, and a suitable amount of Web page contents information is stored in a memory region of each cache server. Depending on the need, it is also necessary to access original Web servers regularly in order to update the information maintained on the cache server. In this case, a policy regarding how the caching should be carried out becomes important because the memory region on the cache server is finite.
In this regard, various cache update policies have been proposed, including a method for coordinating a plurality of cache servers. For instance, in the IETF and W3C which are the standardization organizations for the Internet and the WWW, a protocol called Internet Cache Protocol for enabling cache servers to exchange copies of contents has been standardized.
However, what have been proposed so far are all general cache update policies, and there has been no available technique for realizing effective caching with respect to specific users who make mobile accesses using wireless portable terminals or mobile access users located at specific locations.
For example, in the case of receiving the information delivery service during seamless movements using a wireless connected mobile portable terminal, there can be cases where it is desired to receive geographically relevant information at higher speed or cases where it is desired to deliver geographically relevant information at higher speed with respect to users of mobile portable terminals. Examples of such cases includes a case where it is desired to receive information sent out by stores belonging to a shopping district at higher speed while moving through that shopping district, and a case where it is desired to deliver information specific to a particular area of a big shopping mall at higher speed to those users who have entered that particular area while moving through the shopping mall. There can also be a case where it is desired to cache Web pages that are highly likely to be accessed by a user of a mobile portable terminal at high priority, according to the preferences of the individual user.
However, it has been impossible to realize such services conventionally.